A buffer manager that exploits the tree structure of indexes. More...

#include <buffer_pool.hpp>

Public Member Functions
	BufferPool ()
	Default constructor for a buffer pool. More...

void	postInitialize ()
	Completes the initialization of this buffer pool. More...

void	shutdown ()
	Shuts down this buffer pool. More...

	~BufferPool ()
	Default destructor for a buffer pool. More...

bf_idx	getBlockCount () const noexcept
	Number of buffer frames of this buffer pool. More...

bool	isNoDBMode () const noexcept
	Whether this buffer pool is in NoDB mode. More...

bool	usesWriteElision () const noexcept
	Whether this buffer pool uses write elision. More...

bool	isWarmupDone () const noexcept
	Return whether this buffer pool is already "warmed up". More...

const std::shared_ptr< zero::buffer_pool::Hashtable >	getHashtable () const noexcept
	Returns the hashtable of this buffer pool. More...

const std::shared_ptr< zero::buffer_pool::FreeListLowContention >	getFreeList () const noexcept
	Returns the free list of this buffer pool. More...

const std::shared_ptr< page_cleaner_base >	getPageCleaner () const noexcept
	Returns the page cleaner of this buffer pool. More...

void	wakeupPageCleaner () const

const std::shared_ptr< PAGE_EVICTIONER >	getPageEvictioner () const noexcept
	Returns the page evictioner of this buffer pool. More...

bool	hasDirtyFrames ()
	Whether this buffer pool has dirty buffer frames. More...

void	fixRoot (generic_page *&targetPage, StoreID store, latch_mode_t latchMode, bool conditional, bool virgin)
	Fixes a root B-Tree page in this buffer pool. More...

w_rc_t	fixRootOldStyleExceptions (generic_page *&targetPage, StoreID store, latch_mode_t latchMode, bool conditional, bool virgin)

bool	fixNonRoot (generic_page &targetPage, generic_page parentPage, PageID pid, latch_mode_t latchMode, bool conditional=false, bool virgin=false, bool onlyIfHit=false, bool doRecovery=true, lsn_t emlsn=lsn_t::null)
	Fixes a non-root B-Tree page in this buffer pool. More...

w_rc_t	fixNonRootOldStyleExceptions (generic_page &targetPage, generic_page parentPage, PageID pid, latch_mode_t latchMode, bool conditional=false, bool virgin=false, bool onlyIfHit=false, bool doRecovery=true, lsn_t emlsn=lsn_t::null)

bf_idx	pinForRefix (const generic_page *pinPage)
	Pin a page for a cheaper re-fix. More...

void	refixDirect (generic_page *&targetPage, bf_idx refixIndex, latch_mode_t latchMode, bool conditional)
	Re-fix a pinned page. More...

w_rc_t	refixDirectOldSytleExceptions (generic_page *&targetPage, bf_idx refixIndex, latch_mode_t latchMode, bool conditional)

void	unpinForRefix (bf_idx unpinIndex)
	Unpin a page for re-fix. More...

void	unfix (const generic_page *unfixPage, bool evict=false)
	Unfixes a page in this buffer pool. More...

bf_tree_cb_t &	getControlBlock (bf_idx index) noexcept
	Returns the control block corresponding to a buffer pool index. More...

const bf_tree_cb_t &	getControlBlock (bf_idx index) const noexcept
	Returns the control block corresponding to a buffer pool index. noexcept More...

bf_tree_cb_t &	getControlBlock (const generic_page *page) noexcept
	Returns the control block corresponding to a buffered page. More...

bf_idx	getIndex (const bf_tree_cb_t &controlBlock) const noexcept
	The buffer pool index of a control block. More...

bf_idx	getIndex (const generic_page *page) const noexcept
	The buffer pool index of a buffered page. More...

bf_idx	getRootIndex (StoreID store) const noexcept
	The buffer pool index of a buffered B-Tree root page. More...

generic_page *	getPage (const bf_idx &index) noexcept
	A buffered page at a buffer pool index. More...

const generic_page *	getPage (const bf_idx &index) const noexcept
	A buffered page at a buffer pool index. noexcept More...

bool	isValidIndex (bf_idx index) const noexcept
	Checks the validity of a buffer pool index in this buffer pool. More...

bool	isActiveIndex (bf_idx index) const noexcept
	Checks whether a buffer pool frame is used in this buffer pool. More...

bool	upgradeLatchConditional (const generic_page *page) noexcept
	Upgrade the latch of a page. More...

void	downgradeLatch (const generic_page *page) noexcept
	Downgrade the latch of a page. More...

bool	unswizzlePagePointer (generic_page parentPage, general_recordid_t childSlotInParentPage, PageID childPageID=nullptr)
	Unswizzle a page pointer in a page's parent page. More...

PageID	normalizePID (const PageID pid) const noexcept
	Normalize a page ID. More...

bool	isEvictable (const bf_idx indexToCheck, const bool doFlushIfDirty) noexcept
	Check if a page can be evicted. More...

void	batchPrefetch (PageID startPID, bf_idx numberOfPages) noexcept
	Prefetches a batch of pages into this buffer pool. More...

void	recoverIfNeeded (bf_tree_cb_t &controlBlock, generic_page *page, bool onlyIfDirty=true) noexcept
	Recover buffered page if needed. More...

void	fuzzyCheckpoint (chkpt_t &checkpoint) const noexcept
	Creates a fuzzy checkpoint for this buffer pool. More...

void	sxUpdateChildEMLSN (btree_page_h &parentPage, general_recordid_t childSlotID, lsn_t childEMLSN) const
	Update the EMLSN of a B-Tree child inside its parent page. More...

void	switchParent (PageID childPID, generic_page *newParentPage) noexcept
	Switch the parent page of a buffered B-Tree page in this buffer pool. More...

void	setMediaFailure () noexcept
	MG TODO. More...

void	unsetMediaFailure () noexcept
	MG TODO. More...

PageID	getMediaFailurePID () const noexcept
	MG TODO. More...

bool	isMediaFailure () const noexcept

bool	isMediaFailure (PageID pid) const noexcept
	MG TODO. More...

void	debugDump (std::ostream &o) const
	Dumps some meta data of this buffer pool to an output stream. More...

void	debugDumpPagePointers (std::ostream &o, generic_page *page) const
	Dumps the pointers stored inside a page to an output stream. More...

Private Types
using	RestoreCoord = RestoreCoordinator< std::function< decltype(SegmentRestorer::bf_restore)>>

using	BgRestorer = BackgroundRestorer< RestoreCoord, std::function< void(void)>>

Private Member Functions
bool	_fix (generic_page parentPage, generic_page &targetPage, PageID pid, latch_mode_t latchMode, bool conditional, bool virgin, bool onlyIfHit=false, bool doRecovery=true, lsn_t emlsn=lsn_t::null)
	Fixes a page in this buffer pool. More...

void	_convertToDiskPage (generic_page *page) const noexcept
	Converts an image of a page with swizzled pointers to one without. More...

void	_readPage (PageID pid, generic_page *targetPage, bool fromBackup=false)
	Reads a page from database or backup. More...

void	_deletePage (bf_idx index) noexcept
	Deletes a page from this buffer pool. More...

void	_checkWarmupDone () noexcept
	Decides if this buffer pool is "warmed up". More...

void	_setWarmupDone () noexcept
	Sets this buffer pool to "warmed up". More...

Private Attributes
bf_idx	_blockCount
	Maximum number of pages in this buffer pool. More...

std::array< bf_idx, stnode_page::max >	_rootPages
	Buffer indexes of root pages. More...

std::vector< bf_tree_cb_t, boost::alignment::aligned_allocator< bf_tree_cb_t, sizeof(bf_tree_cb_t)> >	_controlBlocks
	Array of control blocks. More...

generic_page *	_buffer
	Array of buffered pages. More...

std::shared_ptr< Hashtable >	_hashtable
	Allows to locate pages by PageID. More...

std::shared_ptr< FreeListLowContention >	_freeList
	List of unused buffer frames. More...

std::shared_ptr< page_cleaner_base >	_cleaner
	Cleans dirty pages. More...

bool	_cleanerDecoupled
	Use log-based "decoupled" cleaner. More...

std::shared_ptr< PAGE_EVICTIONER >	_evictioner
	Evicts pages. More...

bool	_asyncEviction
	Use a dedicated thread for eviction. More...

bool	_maintainEMLSN
	Maintain EMLSN of B-Tree pages. More...

std::shared_ptr< RestoreCoord >	_restoreCoordinator
	MG TODO. More...

std::shared_ptr< BgRestorer >	_backgroundRestorer
	MG TODO. More...

bool	_useWriteElision
	Use write elision. More...

std::atomic< PageID >	_mediaFailurePID
	MG TODO. More...

bool	_instantRestore
	Use instant restore. More...

bool	_noDBMode
	Use NoDB. More...

bool	_logFetches
	Log page fetches. More...

size_t	_batchSegmentSize
	MG TODO. More...

bool	_batchWarmup
	MG TODO. More...

bool	_warmupDone
	MG TODO. More...

double	_warmupHitRatio
	Hit rate of a "warm" buffer pool. More...

unsigned	_warmupMinFixes
	Minimum number of fixes of a "warm" buffer pool. More...

Static Private Attributes
static thread_local SprIterator	_localSprIter
	Single-page-recovery iterator used for instant restart redo. More...

static thread_local unsigned	_fixCount = 0
	MG TODO. More...

static thread_local unsigned	_hitCount = 0
	MG TODO. More...

Friends
class	::test_bf_tree

class	::bf_tree_cleaner

class	page_cleaner_decoupled

class	::GenericPageIterator

class	FreeListLowContention

class	FreeListHighContention

class	PageEvictioner

template<class selector_class , class filter_class , bool filter_early>
class	PageEvictionerSelectAndFilter

Detailed Description

A buffer manager that exploits the tree structure of indexes.

This buffer manager only deals with tree-structured stores such as B-trees.

Member Typedef Documentation

§ BgRestorer

using zero::buffer_pool::BufferPool::BgRestorer = BackgroundRestorer<RestoreCoord, std::function<void(void)>>

private

§ RestoreCoord

using zero::buffer_pool::BufferPool::RestoreCoord = RestoreCoordinator<std::function<decltype(SegmentRestorer::bf_restore)>>

private

Constructor & Destructor Documentation

§ BufferPool()

zero::buffer_pool::BufferPool::BufferPool ( )

Default constructor for a buffer pool.

Constructs an almost completely initialized buffer pool according to the settings set in ss_m::get_options() .

Postcondition: The buffer pool is partially initialized.

Warning: The buffer pool is only fully initialized after calling postInitialize .

§ ~BufferPool()

zero::buffer_pool::BufferPool::~BufferPool ( )

Default destructor for a buffer pool.

Due to the usage of smart pointers, all this destructor does is implicit.

Warning: Due to forked threads, the buffer pool needs to be shut down before destruction using shutdown .

Member Function Documentation

§ _checkWarmupDone()

zero::buffer_pool::BufferPool::_checkWarmupDone ( )

privatenoexcept

Decides if this buffer pool is "warmed up".

Decides if this buffer pool is "warmed up" by looking at the hit ratio observed for the current thread and the total number of page fixes done by this thread. This is for cases where the dataset fits in main memory and the buffer pool never (or just takes really long to) fill up.

§ _convertToDiskPage()

zero::buffer_pool::BufferPool::_convertToDiskPage ( generic_page * page ) const

privatenoexcept

Converts an image of a page with swizzled pointers to one without.

Converts an image of a page (buffered in this buffer pool) with swizzled pointers to a disk page without swizzled pointers. This is mainly used to write out dirty pages.

Precondition: Hold the latch corresponding to the page in either latch_mode_t::LATCH_SH or latch_mode_t::LATCH_EX .

Parameters

page	The page with swizzled pointers to convert to a disk page.

§ _deletePage()

zero::buffer_pool::BufferPool::_deletePage ( bf_idx index )

privatenoexcept

Deletes a page from this buffer pool.

Makes the buffer frame which corresponds to the specified buffer index unoccupied.

Precondition: The buffer frame corresponding the buffer index is occupied, it is not fixed by any thread and if it contains a non-root B-Tree page, the corresponding pointer is not swizzled in its parent page (the page is not pinned).

Parameters

index The buffer index of the buffer pool frame to be freed.

§ _fix()

zero::buffer_pool::BufferPool::_fix	(	generic_page *	parentPage,
		generic_page *&	targetPage,
		PageID	pid,
		latch_mode_t	latchMode,
		bool	conditional,
		bool	virgin,
		bool	onlyIfHit = `false`,
		bool	doRecovery = `true`,
		lsn_t	emlsn = `lsn_t::null`
	)

private

Fixes a page in this buffer pool.

If pointer swizzling is enabled, this receives the requested page's parent page and efficiently fixes the requested page if the pid is already swizzled by inside the parent page. If it is not already swizzled, it will be swizzled after the execution of this. The optimization is transparent for most of the code because the page ID stored in the parent page is automatically (and atomically) changed to a swizzled pointer by the buffer pool.
If pointer swizzling is disabled, this fixes the requested page in this buffer pool.

Precondition: The parentPage set and latched. Otherwise use fixable_page_h.fix_direct(PageID pid, latch_mode_t mode, bool conditional, bool virgin_page, bool only_if_hit, bool do_recovery) .

Postcondition: The targetPage pointer points to the page which should have been fixed and it is latched in the wanted mode.

Parameters

[in]	parentPage	This is the parent of the page to be fixed. If the page is either represents a root of a B-Tree or is not a B-Tree page this see the prerequisites.
[out]	targetPage	This page should contain the fixed page.
[in]	pid	Page ID of the requested page to be fixed (or buffer pool index with swizzledPIDBit set when swizzled).
[in]	latchMode	The wanted latch mode for the page that should be fixed (only latch_mode_t::LATCH_SH and latch_mode_t::LATCH_EX are allowed here).
[in]	conditional	Whether the fix is conditional (returns immediately even if failed).
[in]	virgin	Whether the page is a new page thus does not have to be read from disk.
[in]	onlyIfHit	The fix is only performed if the requested page is already buffered in this buffer pool (i.e., a page hit occurs)
[in]	doRecovery	Whether recovery should be enabled for this page.
[in]	emlsn	The EMLSN of the requested page.

Returns: If onlyIfHit is set and it is a page miss false , else true .

§ _readPage()

zero::buffer_pool::BufferPool::_readPage	(	PageID	pid,
		generic_page *	targetPage,
		bool	fromBackup = `false`
	)

private

Reads a page from database or backup.

Reads a page from database or backup into a buffer frame of this buffer pool. The source of the page needs to be selected explicitly.

Precondition: Hold the latch corresponding to the targetPage in latch_mode_t::LATCH_EX .

Parameters

pid	The page ID of the page to read.
targetPage	The page should be read into this page image.
fromBackup	Whether the page should be read from the backup or from the database.

§ _setWarmupDone()

zero::buffer_pool::BufferPool::_setWarmupDone ( )

privatenoexcept

Sets this buffer pool to "warmed up".

§ batchPrefetch()

zero::buffer_pool::BufferPool::batchPrefetch	(	PageID	startPID,
		bf_idx	numberOfPages
	)

noexcept

Prefetches a batch of pages into this buffer pool.

Prefetches a continuous batch of pages into this buffer pool using preadv . This allows a faster restore process without traversing the B-Tree.

Parameters

startPID	The page ID of the first page in the continuous batch of pages to prefetch.
numberOfPages	The number of pages to prefetch (page ID of the last prefetched page: `startPID` `+` `numberOfPages` `-` `1` ).

Warning: It is not guaranteed for a non-root B-Tree page that its parent page is also prefetched.; The parent page information of non-root B-Tree pages is not properly set in the hashtable.

§ debugDump()

zero::buffer_pool::BufferPool::debugDump ( std::ostream & o ) const

Dumps some meta data of this buffer pool to an output stream.

Dumps some general meta data of this buffer pool and of the first 1000 buffer pool frames to the specified output stream. See the implementation for more details! The data is multi-lined and cannot be manipulated using stream manipulators.

Parameters

o	The output stream to which the meta data are printed.

Warning: This function is only for debug purposes because it is slow and unsafe.

§ debugDumpPagePointers()

zero::buffer_pool::BufferPool::debugDumpPagePointers	(	std::ostream &	o,
		generic_page *	page
	)		const

Dumps the pointers stored inside a page to an output stream.

Dumps the pointers (accounting for swizzling) of a given page to the specified output stream. See the implementation for more details! The data is single-lined and cannot be manipulated using stream manipulators.

Parameters

o	The output stream to which the pointers are printed.
page	The page whose contained pointers are printed.

Warning: This function is only for debug purposes because it is slow and unsafe.

§ downgradeLatch()

zero::buffer_pool::BufferPool::downgradeLatch ( const generic_page * page )

noexcept

Downgrade the latch of a page.

Downgrade this thread holding the latch of a page in latch_mode_t::LATCH_EX to one holding the latch in latch_mode_t::LATCH_SH .

Parameters

page	The latch corresponding to this page should be downgraded.

§ fixNonRoot()

zero::buffer_pool::BufferPool::fixNonRoot	(	generic_page *&	targetPage,
		generic_page *	parentPage,
		PageID	pid,
		latch_mode_t	latchMode,
		bool	conditional = `false`,
		bool	virgin = `false`,
		bool	onlyIfHit = `false`,
		bool	doRecovery = `true`,
		lsn_t	emlsn = `lsn_t::null`
	)

Fixes a non-root B-Tree page in this buffer pool.

If pointer swizzling is enabled, this receives the requested page's parent page and efficiently fixes the requested page if the pid is already swizzled by inside the parent page. If it is not already swizzled, it will be swizzled after the execution of this. The optimization is transparent for most of the code because the page ID stored in the parent page is automatically (and atomically) changed to a swizzled pointer by the buffer pool.
If pointer swizzling is disabled, this fixes the requested page in this buffer pool.

Precondition: The parentPage set and latched. Otherwise use fixable_page_h.fix_direct(PageID pid, latch_mode_t mode, bool conditional, bool virgin_page, bool only_if_hit, bool do_recovery) .

Postcondition: The targetPage pointer points to the page which should have been fixed and it is latched in the wanted mode.

Parameters

[out]	targetPage	This page should contain the fixed page.
[in]	parentPage	This is the parent of the page to be fixed. If the page is either represents a root of a B-Tree or is not a B-Tree page this see the prerequisites.
[in]	pid	Page ID of the requested page to be fixed (or buffer pool index with swizzledPIDBit set when swizzled).
[in]	latchMode	The wanted latch mode for the page that should be fixed (only latch_mode_t::LATCH_SH and latch_mode_t::LATCH_EX are allowed here).
[in]	conditional	Whether the fix is conditional (returns immediately even if failed).
[in]	virgin	Whether the page is a new page thus does not have to be read from disk.
[in]	onlyIfHit	The fix is only performed if the requested page is already buffered in this buffer pool (i.e., a page hit occurs)
[in]	doRecovery	Whether recovery should be enabled for this page.
[in]	emlsn	The EMLSN of the requested page.

Returns: If onlyIfHit is set and it is a page miss false , else true .

§ fixNonRootOldStyleExceptions()

w_rc_t BufferPool::fixNonRootOldStyleExceptions	(	generic_page *&	targetPage,
		generic_page *	parentPage,
		PageID	pid,
		latch_mode_t	latchMode,
		bool	conditional = `false`,
		bool	virgin = `false`,
		bool	onlyIfHit = `false`,
		bool	doRecovery = `true`,
		lsn_t	emlsn = `lsn_t::null`
	)

§ fixRoot()

zero::buffer_pool::BufferPool::fixRoot	(	generic_page *&	targetPage,
		StoreID	store,
		latch_mode_t	latchMode,
		bool	conditional,
		bool	virgin
	)

Fixes a root B-Tree page in this buffer pool.

Fixes an existing (not virgin) root B-Tree page of a given store in this buffer pool.

Postcondition: The targetPage pointer points to the page which should have been fixed and it is latched in the wanted mode.

Parameters

[out]	targetPage	This page should contain the fixed page.
[in]	store	Store ID of the store whose root B-Tree page is requested to be fixed.
[in]	latchMode	The wanted latch mode for the page that should be fixed (only latch_mode_t::LATCH_SH and latch_mode_t::LATCH_EX are allowed here).
[in]	conditional	Whether the fix is conditional (returns immediately even if failed).
[in]	virgin	Whether the page is a new page thus does not have to be read from disk.

§ fixRootOldStyleExceptions()

w_rc_t BufferPool::fixRootOldStyleExceptions	(	generic_page *&	targetPage,
		StoreID	store,
		latch_mode_t	latchMode,
		bool	conditional,
		bool	virgin
	)

§ fuzzyCheckpoint()

zero::buffer_pool::BufferPool::fuzzyCheckpoint ( chkpt_t & checkpoint ) const

noexcept

Creates a fuzzy checkpoint for this buffer pool.

Adds the information required for a fuzzy checkpoint of this buffer pool to the given checkpoint. A fuzzy checkpoint of this buffer pool contains all the page IDs of potentially dirty pages buffered in this buffer pool together with their LSNs.

Postcondition: The checkpoint contains a fuzzy checkpoint of this buffer pool.

Parameters

[in,out] checkpoint A fuzzy checkpoint.

§ getBlockCount()

bf_idx zero::buffer_pool::BufferPool::getBlockCount ( ) const

inlinenoexcept

Number of buffer frames of this buffer pool.

Returns: The number of buffer pool frames (_blockCount) of this buffer pool.

§ getControlBlock() [1/3]

bf_tree_cb_t & zero::buffer_pool::BufferPool::getControlBlock ( bf_idx index )

inlinenoexcept

Returns the control block corresponding to a buffer pool index.

Returns the control block which corresponds to the buffer frame at the given buffer pool index. Due to the allocation scheme used in _controlBlocks , it is not trivial (but possible in constant time) to find the requested control block.

Parameters

index A buffer pool index corresponding to a buffer frame of this buffer pool.

Returns: The control block corresponding to the buffer frame of the given buffer pool index.

§ getControlBlock() [2/3]

const bf_tree_cb_t& zero::buffer_pool::BufferPool::getControlBlock ( bf_idx index ) const

inlinenoexcept

Returns the control block corresponding to a buffer pool index. noexcept

Returns the control block which corresponds to the buffer frame at the given buffer pool index. Due to the allocation scheme used in _controlBlocks , it is not trivial (but possible in constant time) to find the requested control block.

Parameters

index A buffer pool index corresponding to a buffer frame of this buffer pool.

Returns: The control block corresponding to the buffer frame of the given buffer pool index. noexcept

§ getControlBlock() [3/3]

bf_tree_cb_t & zero::buffer_pool::BufferPool::getControlBlock ( const generic_page * page )

inlinenoexcept

Returns the control block corresponding to a buffered page.

Returns the control block which corresponds to the buffer frame of a given buffered page. Due to the allocation scheme used in _controlBlocks , it is not trivial (but possible in constant time) to find the requested control block.

Parameters

page	A page buffered in this buffer pool.

Returns: The control block corresponding to the buffer frame of the given buffered page.

Warning: Unwanted behaviour if the given page is not buffered in this buffer pool!

§ getFreeList()

zero::buffer_pool::BufferPool::getFreeList ( ) const

inlinenoexcept

Returns the free list of this buffer pool.

Returns: The free list holding a queue of unoccupied buffer frames of this buffer pool.

§ getHashtable()

zero::buffer_pool::BufferPool::getHashtable ( ) const

inlinenoexcept

Returns the hashtable of this buffer pool.

Returns: The hashtable mapping page IDs of pages buffered in this buffer pool to the corresponding buffer indexes of them and their parent pages.

§ getIndex() [1/2]

zero::buffer_pool::BufferPool::getIndex ( const bf_tree_cb_t & controlBlock ) const

inlinenoexcept

The buffer pool index of a control block.

Returns the buffer pool index to which the given control block corresponds to.

Parameters

controlBlock A control block of this buffer pool.

Returns: The buffer pool index to which controlBlock corresponds to.

§ getIndex() [2/2]

zero::buffer_pool::BufferPool::getIndex ( const generic_page * page ) const

inlinenoexcept

The buffer pool index of a buffered page.

Returns the buffer pool index in which the given buffered page is buffered in.

Parameters

page	A page buffered in this buffer pool.

Returns: The buffer pool index in which page is buffered in.

§ getMediaFailurePID()

zero::buffer_pool::BufferPool::getMediaFailurePID ( ) const

inlinenoexcept

MG TODO.

MG TODO

Returns: MG TODO

§ getPage() [1/2]

generic_page * zero::buffer_pool::BufferPool::getPage ( const bf_idx & index )

inlinenoexcept

A buffered page at a buffer pool index.

Returns the page which is buffered at a given buffer pool index in this buffer pool.

Parameters

index A buffer index of this buffer pool.

Returns: The page which is buffered in the buffer frame with buffer index index .

Note: Mainly for debugging!

§ getPage() [2/2]

const generic_page* zero::buffer_pool::BufferPool::getPage ( const bf_idx & index ) const

inlinenoexcept

A buffered page at a buffer pool index. noexcept

Returns the page which is buffered at a given buffer pool index in this buffer pool.

Parameters

index A buffer index of this buffer pool.

Returns: The page which is buffered in the buffer frame with buffer index index .

Note: Mainly for debugging! noexcept

§ getPageCleaner()

zero::buffer_pool::BufferPool::getPageCleaner ( ) const

inlinenoexcept

Returns the page cleaner of this buffer pool.

Returns: The page cleaner thread responsible to write-back dirty pages of this buffer pool.

§ getPageEvictioner()

zero::buffer_pool::BufferPool::getPageEvictioner ( ) const

noexcept

Returns the page evictioner of this buffer pool.

Returns: The page evictioner (thread) responsible evict pages from this buffer pool once its full.

§ getRootIndex()

zero::buffer_pool::BufferPool::getRootIndex ( StoreID store ) const

inlinenoexcept

The buffer pool index of a buffered B-Tree root page.

Returns the buffer pool index in which a B-Tree root page specified by its Store ID is buffered in.

Parameters

store The Store ID of the requested B-Tree root page.

Returns: The buffer pool index where the requested B-Tree root page is buffered in this buffer pool or 0 if it is currently not buffered in this buffer pool.

§ hasDirtyFrames()

zero::buffer_pool::BufferPool::hasDirtyFrames ( )

Whether this buffer pool has dirty buffer frames.

Checks each frame of the buffer pool whether it contains a page and whether this page is dirty inside the buffer pool frame. In NoDB mode, pages cannot be dirty.

Returns: true if this buffer pool contains dirty buffer frames, false else.

§ isActiveIndex()

zero::buffer_pool::BufferPool::isActiveIndex ( bf_idx index ) const

inlinenoexcept

Checks whether a buffer pool frame is used in this buffer pool.

Whether the given buffer pool index is in the range of valid buffer pool indexes of this buffer pool (0 is invalid and too large indexes are invalid, too) and whether it is occupied by a page.

Precondition: Hold the latch corresponding to the buffer pool index in latch_mode_t::LATCH_SH or latch_mode_t::LATCH_EX .

Parameters

index The buffer pool index to be checked.

Returns: Whether index is a valid buffer pool index in this buffer pool and whether a page is buffered in the corresponding buffer frame.

§ isEvictable()

zero::buffer_pool::BufferPool::isEvictable	(	const bf_idx	indexToCheck,
		const bool	doFlushIfDirty
	)

noexcept

Check if a page can be evicted.

The following conditions make a page unevictable:

There is no page in the buffer frame (bf_tree_cb_t::_used == false).
It is the store node page (generic_page_h::tag() == page_tag_t::t_stnode_p).
It is the root page of a B-Tree (generic_page_h::tag() == page_tag_t::t_btree_p && generic_page_h::pid() == btree_page_h::root()).
It is an inner page of a B-Tree and swizzling is enabled (POINTER_SWIZZLER::usesPointerSwizzling && generic_page_h::tag() == page_tag_t::t_btree_p && ! btree_page_h::is_leaf() ).
We exclude those as we do not support unswizzling and as we do not know if inner pages of a B-Tree might contain swizzled pointers.
It is a page of a B-Tree with foster child (POINTER_SWIZZLER::usesPointerSwizzling && generic_page_h::tag() == page_tag_t::t_btree_p && btree_page_h::get_foster()) != 0).
We exclude those as we do not support unswizzling.
It is a dirty page that needs to be cleaned by the page cleaner (( doFlushIfDirty || _noDBMode || _useWriteElision ) && bf_tree_cb_t::is_dirty())
If noDB or write elision is used, a page doesn't need to be flushed before eviction and if the evictioner flushes dirty pages, those can be evicted as well.
There is no page in the buffer pool frame - it is unused (! bf_tree_cb_t::_used ).
It is pinned (! bf_tree_cb_t::_pin_cnt != 0).
The page is either pinned or it gets currently evicted by another thread.

Precondition: The buffer frame with index indexToCheck is latched in latch_mode_t::LATCH_SH or latch_mode_t::LATCH_EX mode by this thread.

Remarks: The example implementations for the conditions are given in the documentation because it is hard to figure out which pages cannot be evicted.

Parameters

indexToCheck	The index of the buffer frame that is supposed to be freed by evicting the contained page.
doFlushIfDirty	`true` if the page gets flushed during the eviction, `false` else.

Returns: true if the page could be evicted, false else.

§ isMediaFailure() [1/2]

bool zero::buffer_pool::BufferPool::isMediaFailure ( ) const

inlinenoexcept

§ isMediaFailure() [2/2]

bool zero::buffer_pool::BufferPool::isMediaFailure ( PageID pid ) const

inlinenoexcept

MG TODO.

MG TODO

Parameters

pid MG TODO

Returns: MG TODO

§ isNoDBMode()

zero::buffer_pool::BufferPool::isNoDBMode ( ) const

inlinenoexcept

Whether this buffer pool is in NoDB mode.

Returns: true if this buffer pool is in NoDB mode (_noDBMode ), false else.

§ isValidIndex()

zero::buffer_pool::BufferPool::isValidIndex ( bf_idx index ) const

inlinenoexcept

Checks the validity of a buffer pool index in this buffer pool.

Whether the given buffer pool index is in the range of valid buffer pool indexes of this buffer pool (0 is invalid and too large indexes are invalid, too).

Parameters

index The buffer pool index to be checked.

Returns: Whether index is a valid buffer pool index in this buffer pool.

§ isWarmupDone()

bool zero::buffer_pool::BufferPool::isWarmupDone ( ) const

inlinenoexcept

Return whether this buffer pool is already "warmed up".

Returns whether this buffer pool is already "warmed up". Further details on the meaning of "warmed up" can be found at _checkWarmupDone() .

Returns: False, if the warmup of this buffer pool is ongoing, true else.

§ normalizePID()

zero::buffer_pool::BufferPool::normalizePID ( const PageID pid ) const

inlinenoexcept

Normalize a page ID.

Normalizes the given page ID to an actual page ID (for vol_t ). If the page ID is a buffer pool index (in case of swizzling) then it returns the page ID of the page on disk, otherwise it returns the page ID as it is.

Precondition: Hold the latch corresponding to the parent page in latch_mode_t::LATCH_SH or latch_mode_t::LATCH_EX ?

Parameters

pid	The page ID to normalize.

Returns: The corresponding page ID to a vol_t page.

§ pinForRefix()

zero::buffer_pool::BufferPool::pinForRefix ( const generic_page * pinPage )

Pin a page for a cheaper re-fix.

Adds an additional pin count for the given pinPage . This is used to re-fix the page later without parent pointer. See refixDirect(generic_page*& targetPage, bf_idx refixIndex, latch_mode_t latchMode, bool conditional) why we need this feature.

Precondition: The buffer frame corresponding to pinPage is already latched by this thread.

Postcondition: The page cannot be evicted because it is pinned by this thread.

Parameters

[in] pinPage The page that is currently latched and will be re-fixed later.

Returns: Buffer frame index of the pinPage in this buffer pool. Use this value for the subsequent calls to refixDirect(generic_page*& targetPage, bf_idx refixIndex, latch_mode_t latchMode, bool conditional) and unpinForRefix(bf_idx unpinIndex) .

Warning: Never forget to call a corresponding unpinForRefix(bf_idx unpinIndex) because otherwise the pinPage will be in this buffer pool forever.

§ postInitialize()

void zero::buffer_pool::BufferPool::postInitialize ( )

Completes the initialization of this buffer pool.

Completes the initialization of this buffer pool which was started during its construction.

Precondition: vol_t::_alloc_cache needs to be initialized before.

Postcondition: The buffer pool is fully initialized. All the required auxiliary threads are running.

§ recoverIfNeeded()

zero::buffer_pool::BufferPool::recoverIfNeeded	(	bf_tree_cb_t &	controlBlock,
		generic_page *	page,
		bool	onlyIfDirty = `true`
	)

noexcept

Recover buffered page if needed.

Recovers a page—buffered in this buffer pool—if needed using the _localSprIter . It is not needed when recovery is disabled in general or when it is disabled for the particular page. It is possibly needed when it is explicitly requested (onlyIfTrue == false ) or when the page is dirty.

Precondition: Hold the latch corresponding to the control block in latch_mode_t::LATCH_EX .

Postcondition: If recovery is enabled, the page is not dirty and a log record of type fetch_page_log was created if _logFetches is true .

Parameters

controlBlock	The control block of the page to recover if needed.
page	The buffered page to recover if needed.
onlyIfDirty	Whether the page should be recovered even though it is not dirty.

§ refixDirect()

zero::buffer_pool::BufferPool::refixDirect	(	generic_page *&	targetPage,
		bf_idx	refixIndex,
		latch_mode_t	latchMode,
		bool	conditional
	)

Re-fix a pinned page.

Re-fixes a page without the parent pointer which was pinned for refix (pinForRefix(const generic_page* pinPage) ) before.

Parameters

[out]	targetPage	This page should contain the re-fixed page.
[in]	refixIndex	Buffer pool index of the requested page to be re-fixed.
[in]	latchMode	The wanted latch mode for the page that should be re-fixed (only latch_mode_t::LATCH_SH and latch_mode_t::LATCH_EX are allowed here).
[in]	conditional	Whether the re-fix is conditional (returns immediately even if failed).

§ refixDirectOldSytleExceptions()

w_rc_t BufferPool::refixDirectOldSytleExceptions	(	generic_page *&	targetPage,
		bf_idx	refixIndex,
		latch_mode_t	latchMode,
		bool	conditional
	)

§ setMediaFailure()

void zero::buffer_pool::BufferPool::setMediaFailure ( )

noexcept

MG TODO.

MG TODO

Precondition: MG TODO

Postcondition: MG TODO

§ shutdown()

void zero::buffer_pool::BufferPool::shutdown ( )

Shuts down this buffer pool.

Stops the threads forked by this buffer pool to allow destruction without leaving those threads running.

Postcondition: Threads forked by the buffer pool are stopped. The buffer pool is not able to work properly anymore.

§ switchParent()

zero::buffer_pool::BufferPool::switchParent	(	PageID	childPID,
		generic_page *	newParentPage
	)

noexcept

Switch the parent page of a buffered B-Tree page in this buffer pool.

For each buffered non-root B-Tree page, the buffer pool also stores the buffer pool index of the buffer frame where the corresponding parent page is buffered. Therefore, this information needs to be updated once the parent page of such a page is changed. That is what this function does.

Precondition: Hold the latch corresponding to the old and new parent page in either latch_mode_t::LATCH_SH or latch_mode_t::LATCH_EX .

Parameters

childPID	The page ID of the B-Tree page whose parent is switched.
newParentPage	The new parent page.

§ sxUpdateChildEMLSN()

zero::buffer_pool::BufferPool::sxUpdateChildEMLSN	(	btree_page_h &	parentPage,
		general_recordid_t	childSlotID,
		lsn_t	childEMLSN
	)		const

Update the EMLSN of a B-Tree child inside its parent page.

Sets the EMLSN of a B-Tree child in the corresponding slot of its parent page. This uses a system transaction for the purpose.

Precondition: Hold the latch corresponding to the parent page in either latch_mode_t::LATCH_SH or latch_mode_t::LATCH_EX .

Postcondition: A log record of type update_emlsn_log was created.

Parameters

parentPage	The parent page buffered in this buffer pool.
childSlotID	The corresponding slot ID of the child within `parentPage` .
childEMLSN	The new EMLSN of the child page requested to be written in the parent page.

§ unfix()

zero::buffer_pool::BufferPool::unfix	(	const generic_page *	unfixPage,
		bool	evict = `false`
	)

Unfixes a page in this buffer pool.

Unfixes the given page in this buffer pool by releasing its latch, and, if requested, evicting the page.

Parameters

[in]	unfixPage	The page that should be unfixed.
[in]	evict	Whether the unfixed page should be explicitly evicted if possible.

§ unpinForRefix()

zero::buffer_pool::BufferPool::unpinForRefix ( bf_idx unpinIndex )

Unpin a page for re-fix.

Removes the additional pin count added by the call to pinForRefix(const generic_page* pinPage) from the buffer frame corresponding to the given buffer frame index.

Precondition: The page cannot be evicted because it is pinned by this thread.

Postcondition: If no other thread pinned this page, it can be evicted.

Parameters

[in] unpinIndex Buffer pool index of the page to be unpin for refix.

§ unsetMediaFailure()

void zero::buffer_pool::BufferPool::unsetMediaFailure ( )

noexcept

MG TODO.

MG TODO

Precondition: MG TODO

Postcondition: MG TODO

MG TODO

Returns: MG TODO

§ unswizzlePagePointer()

zero::buffer_pool::BufferPool::unswizzlePagePointer	(	generic_page *	parentPage,
		general_recordid_t	childSlotInParentPage,
		PageID *	childPageID = `nullptr`
	)

Unswizzle a page pointer in a page's parent page.

Tries to unswizzle the given child page (childSlotInParentPage ) from the parent page (parentPage ). If, for some reason, unswizzling was impossible or troublesome, gives up and returns false .

Precondition: The parent page is latched in any mode and the child page is latched in mode latch_mode_t::LATCH_EX.

Parameters

[in]	parentPage	The parent page where to unswizzle the child page.
[in]	childSlotInParentPage	The slot within the parent page where to find the swizzled pointer to the child page.
[in,out]	childPageID	If it wasn't set to the `nullptr`, the unswizzled PageID of the child page is returned.

Returns: false if the unswizzling was not successful, else true.

§ upgradeLatchConditional()

zero::buffer_pool::BufferPool::upgradeLatchConditional ( const generic_page * page )

noexcept

Upgrade the latch of a page.

Upgrade this thread holding the latch of a page in latch_mode_t::LATCH_SH to one holding the latch in latch_mode_t::LATCH_EX without waiting.

Parameters

page	The latch corresponding to this page should be upgraded.

Returns: If the latch is already held in latch_mode_t::LATCH_EX or if the latch could be upgraded immediately true, else false .

§ usesWriteElision()

zero::buffer_pool::BufferPool::usesWriteElision ( ) const

inlinenoexcept

Whether this buffer pool uses write elision.

Returns: true if this buffer pool uses write elision (_useWriteElision ), false else.

§ wakeupPageCleaner()

void zero::buffer_pool::BufferPool::wakeupPageCleaner ( ) const

template<class selector_class , class filter_class , bool filter_early>

friend class PageEvictionerSelectAndFilter

friend

Member Data Documentation

§ _asyncEviction

zero::buffer_pool::BufferPool::_asyncEviction

private

Use a dedicated thread for eviction.

Set if a dedicated thread should be used for page eviction. If a dedicated thread is used, threads encountering a full buffer pool wakeup this page eviction thread and wait until there is a buffer index of an unoccupied buffer frame available for them in the _freeList . If no dedicated thread is used, the first thread encountering a full buffer pool runs the eviction before it continues with its transaction.

Note: One run of the evictioner might evict many pages (batch eviction) therefore such a run might take a long time.

§ _freeList

zero::buffer_pool::BufferPool::_freeList

private

List of unused buffer frames.

A queue containing the indexes of currently unoccupied buffer frames of this buffer pool.

Note: It could be any synchronized data structure but a queue is required for some of the page eviction strategies like CLOCK.

§ _hashtable

zero::buffer_pool::BufferPool::_hashtable

private

Allows to locate pages by PageID.

A hashtable which maps the PageID of page buffered in this buffer pool to the buffer frame index where it is located in. For each buffered page, it also contains the buffer frame index of its parent page (if it's a non-root B-Tree page).

§ _hitCount

zero::buffer_pool::BufferPool::_hitCount = 0

staticprivate

MG TODO.

MG TODO

§ _instantRestore

zero::buffer_pool::BufferPool::_instantRestore

private

Use instant restore.

Set if instant restore should be used by this buffer pool. MG TODO

§ _localSprIter

zero::buffer_pool::BufferPool::_localSprIter

staticprivate

Single-page-recovery iterator used for instant restart redo.

MG TODO

See also: recoverIfNeeded

The documentation for this class was generated from the following files:

src/sm/buffer_pool.hpp
src/sm/buffer_pool.cpp

Public Member Functions

Private Types

Private Member Functions

Private Attributes

Static Private Attributes

Friends

Detailed Description

Member Typedef Documentation

§ BgRestorer

§ RestoreCoord

Constructor & Destructor Documentation

§ BufferPool()

§ ~BufferPool()

Member Function Documentation

§ _checkWarmupDone()

§ _convertToDiskPage()

§ _deletePage()

§ _fix()

§ _readPage()

§ _setWarmupDone()

§ batchPrefetch()

§ debugDump()

§ debugDumpPagePointers()

§ downgradeLatch()

§ fixNonRoot()

§ fixNonRootOldStyleExceptions()

§ fixRoot()

§ fixRootOldStyleExceptions()

§ fuzzyCheckpoint()

§ getBlockCount()

§ getControlBlock() [1/3]

§ getControlBlock() [2/3]

§ getControlBlock() [3/3]

§ getFreeList()

§ getHashtable()

§ getIndex() [1/2]

§ getIndex() [2/2]

§ getMediaFailurePID()

§ getPage() [1/2]

§ getPage() [2/2]

§ getPageCleaner()

§ getPageEvictioner()

§ getRootIndex()

§ hasDirtyFrames()

§ isActiveIndex()

§ isEvictable()

§ isMediaFailure() [1/2]

§ isMediaFailure() [2/2]

§ isNoDBMode()

§ isValidIndex()

§ isWarmupDone()

§ normalizePID()

§ pinForRefix()

§ postInitialize()

§ recoverIfNeeded()

§ refixDirect()

§ refixDirectOldSytleExceptions()

§ setMediaFailure()

§ shutdown()

§ switchParent()

§ sxUpdateChildEMLSN()

§ unfix()

§ unpinForRefix()

§ unsetMediaFailure()

§ unswizzlePagePointer()

§ upgradeLatchConditional()

§ usesWriteElision()

§ wakeupPageCleaner()

Friends And Related Function Documentation

§ ::bf_tree_cleaner

§ ::GenericPageIterator

§ ::test_bf_tree

§ FreeListHighContention

§ FreeListLowContention

§ page_cleaner_decoupled

§ PageEvictioner

§ PageEvictionerSelectAndFilter

Member Data Documentation

§ _asyncEviction

§ _backgroundRestorer